Transmission oil for construction machines widely used in the world have been formulated with ZnDTP due to its multifunction in oxidation inhibition, corrosion prevention, and wear inhibition. Recent trend in downsizing the transmission to achieve better efficiency and lower cost generates a high pressure and high temperature environment in the transmission system. ZnDTP is known to decompose by reaction with water to form zinc polyphosphates, water soluble phosphate and alkyl sulfides, which is the cause of sludge formation. High pressure and high temperature environment can worsen the ZnDTP decomposition. Therefore, the presence of ZnDTP can cause clogging of the clutches under extraordinary surface pressure and high temperature conditions, which decreases friction coefficient.
The present invention relates to Zinc-free transmission oil for construction machinery. The lubricating oil composition exhibit both improved friction characteristics and extreme pressure performance even without ZnDTP.
In general, the following patent art teaches elements of the proposed invention, but none of them teach a dithiophosphorylated carboxylic acid compound in combination with a succinimide dispersant derived from a polyisobutylene group of 1200 molecular weight or less.
U.S. Pat. No. 6,225,266 teaches a Zinc-free lubricant composition for lubricating a continuously variable transmission, which comprises a mixture of a major amount of a lubricating oil and an effective amount of a performance enhancing additive combination comprising: (a) an ashless dispersant; (b) at least one organic phosphite; (c) a calcium detergent; (d) one or more friction modifiers selected from the group consisting of: succinimides and ethoxylated amines; and (e) a primary amide of a long chain carboxylic acid.
U.S. Pat. No. 6,337,309 teaches a zinc-free lubricating composition for lubricating a continuously variable transmission which comprises a mixture of a major amount of a lubricating oil and an effective amount of a performance enhancing additive combination comprising: (a) an ashless polyisobutenyl succinimide dispersant; (b) at least one organic thioether phosphite; (c) a calcium phenate overbased detergent at a concentration such that the total amount of calcium in the fluid is less than about 500 ppm; (d) friction modifiers comprising one or more succinimides and one or more ethoxylated amines; and (e) a primary amide of a long chain carboxylic acid.
US patent application number US20060276352 teaches a a lubricating composition containing (a) an oil soluble phosphorus amine salt; (b) about 0.0001 wt % to about 0.5 wt % of a metal containing detergent package comprising a phenate and a sulphonate; (c) a dispersant; (d) a dispersant viscosity modifier; (e) a metal deactivator; and (f) an oil of lubricating viscosity, wherein the lubricating composition contains less than about 0.25 wt % of a metal dialkyldithiophosphate.
US patent application number US20060264340 teaches a method of lubricating a dual clutch transmission employing a plurality of wet clutches by a lubricating fluid includes a base oil, a succinimide dispersant, a succinimide friction modifier, and a phosphonate.
U.S. Pat. No. 6,756,346 teaches a lubricating oil composition comprising (I) 100 pbw of a base oil, (II) an antiwear agent comprising (i) from 0.05 to 10 pbw of a phosphorothionate and from 0.01 to 1.0 pbw of an amine salt of phosphorus compound and/or (ii) from 0.05 to 10 pbw of a dithiophosphate, and (III) a rust preventing agent comprising from 0.01 to 1.0 pbw of an amide obtained by reacting a polyalkylene polyamine and a carboxylic acid having from 4 to 30 carbon atoms, and the use of such lubricating composition.
U.S. Pat. No. 5,942,470 teaches gear oil and gear oil additive concentrates of enhanced positraction performance, which comprise: (i) at least one oil-soluble sulfur-containing extreme pressure or antiwear agent; (ii) at least one oil-soluble amine salt of a partial ester of an acid of phosphorus; and (iii) at least one oil-soluble succinimide of specific structure. These compositions preferably contain one or more of the following additional components: (iv) at least one amine salt of a carboxylic acid; (v) at least one nitrogen-containing ashless dispersant; and (vi) at least one trihydrocarbyl ester of a pentavalent acid of phosphorus.
US patent application number US20100152078 teaches a lubricating oil composition comprising a sulfurized neopentyl glycol phosphate, a substituted succinimide, a reaction product of an alkyl dicarboxylic acid or anhydride and ammonia, a fatty amine ethoxylate, an oleamide, and dodecyl succinic acid.
European patent number EP1055722 teaches an oil composition for non-stage transmissions which is obtained by incorporating (b) a polymethacrylate, (c) the phenate or a sulfonate of an alkaline earth metal, (d) an imide compound, (e) an (alkyl)phenyl(thio)phosphate, (f) zinc dithiophosphate, and (g) a fatty acid amide compound into (a) a lube base oil.
U.S. Pat. No. 6,534,451 teaches a power transmission fluid composition comprising an ashless dispersant, a friction modifier, an antioxidant, a viscosity modifier and an antiwear agent which is the product formed by reacting elemental sulfur and a dialkylphosphite.
European patent number EP0769546 teaches a lubricating oil composition comprising a boron containing overbased material, a phosphorus compound, a borated friction modifier, a thiocarbamate and a dispersant viscosity modifier.
US patent application number US20040192562 teaches a lubricating oil composition which comprises calcium salicylate having a base number of 50 to 300 mgKOH/g in an amount of 0.005 to 0.07 percent by mass in terms of calcium, an SP type extreme pressure additive in an amount of 0.005 to 0.07 percent by mass in terms of phosphorous, one or more compounds selected from the group consisting of specific succinimide compounds below in an amount of 0.1 to 6 percent by mass, and a boron-containing ashless dispersant in an amount of 0.001 to 0.05 percent by mass in terms of boron, based on the total mass of the composition.
US patent application number US2014162919 teaches a lubricant composition for a full transmission system, comprising an ashless dispersant; a friction modifier; a phosphorus-containing antiwear agent; an antirust additive; a sulfur-containing extreme-pressure additive; a metal deactivation additive; a viscosity index improver; and a pour-point depressant.
It is therefore desirable for a Zinc-free transmission oil for construction machinery. The present invention is directed to a Zinc-free transmission lubricating oil composition which exhibit both improved friction characteristics and extreme pressure performance even without ZnDTP.